The technology described in this disclosure relates generally to semiconductor devices and more particularly to fabrication of semiconductor devices.
Light sensitive materials (e.g., photoresist) are often applied to a semiconductor wafer for device fabrication. For example, a wafer is held on a rotating chuck, and the diameter of the chuck is slightly less than the diameter of the wafer. Liquid light sensitive materials are applied onto a top surface of a wafer when the wafer is spinning with the chuck. The light sensitive materials spread radially outward from the center of the wafer towards the edge to coat the top of the wafer. Ideally, excess light sensitive materials are ejected from the edge of the wafer. In practice, however, some excess light sensitive materials often tend to collect at and form one or more beads along the edge of the wafer. Usually, an ARC lamp is used to emit light beams on an edge portion of the wafer for edge bead removal. An ARC lamp usually involves two electrodes (e.g., made from tungsten) separated by a gas in a bulb and the gas contained in the bulb may include neon, argon, xenon, krypton, sodium, metal halide, and/or mercury.